The invention relates to an air cooled electric motor having a stator, a rotor, end plates and a fan, for higher protection systems than IP 23.
Standard electric motors for individual protection systems, for example, IP 23 or IP 54 (DIN 40050) are very different in construction. This means that special components must be produced and stored for each motor construction. The reason for the different constructions is the various regulations which must be observed concerning the movement of the cooling air, in dependence on the protection system. The electric motor is used in the higher protection systems where components of a machine must be so protected against foreign bodies or the ingress of water that it results in not enough cooling air being supplied to the winding heads of the coils in the stator. Frequently the construction having cooling fins on the external periphery is selected for these higher protection systems. A fan attached to an end face of the motor supplies cooling air in the axial direction through the channels which are formed between the fins and are open at the top, although the cooling result at the start and end of the motor differs greatly. Due to the cooling channels open at the top, the cooling air passes over and cools the casing jacket only over a portion of its length, while the cooling air increasingly escapes upwards out of the channels in the axial direction of the casing, so that the end of the motor casing is inadequately cooled. With the lower protection systems, the fan attached to an end face of the motor sucks or forces surrounding air through openings in the end plate disposed at the axial end of the motor remote from the fan and forces such air in the axial direction through the free spaces in the motor. Examples of the different construction of conventional standard motors are shown in FIGS. 1 and 2. FIG. 1 illustrates an electric motor of low protection system, for example, IP 23, while FIG. 2 shows a standard motor of higher protection system, for example, IP 54. As can be readily seen, in the two kinds of standard motor the casings are very differently constructed.